FRIDAY, April 18, 2014 (HealthDay News) -- Body shape -- whether a woman is wide at the waistline -- is not in itself a risk factor for breast cancer, according to a large new study.

But overall body weight is a factor, the researchers added.

Previous studies have suggested that being "apple-shaped" or having excess fat around the waist is linked to a slew of health problems, like heart disease and type 2 diabetes.

But the new study conducted by researchers at the American Cancer Society found that being apple-shaped is not any riskier than being "pear-shaped" with more fat on the hips, thighs and buttocks, in terms of breast cancer.

What is riskier for postmenopausal women, the researchers found, is having a high body-mass index. BMI is a measurement used to help determine if people are underweight, overweight or a normal for their height.

Not only is BMI a quick way to figure out if people are a healthy weight for their height, it can also be used to predict their health risks, researchers say.

The new study involved nearly 29,000 women. Of these participants, most were white and 1,088 were diagnosed with invasive breast cancer over an average of 11.5 years of follow-up.

The researchers found that a larger waist circumference was linked to a greater risk for breast cancer among postmenopausal women. However, they report, that link disappeared once the women's BMI was taken into account.

"The message is that if you have a high BMI, regardless if you are pear- or apple-shaped, you are at higher risk of breast cancer," study leader Mia Gadet said in a cancer society news release. "Most prior studies on this issue looked at BMI or at waist circumference, but had not looked at them together. This study brings some clarity to the association between obesity and risk of breast cancer."

While the study found an association between being overweight and having a higher risk for breast cancer in women, it did not prove a cause-and-effect relationship.

The researchers suggested their findings, published in the April issue of Cancer Causes & Control, could help women gain a better understanding of the risk factors for breast cancer.

"We know being overweight, particularly when the weight gain happened during adulthood, is one of the important modifiable risk factors for breast cancer in postmenopausal women," Gadet noted. "This new data indicates it's not what shape you are, it's what kind of shape you are in that probably ought to be their focus."